Oil prices will stay low, barring a geopolitical crisis. We may get one soon. ISIS seizing control of Saudi Arabia's oil fields would drive crude back above $100 in a heartbeat.

"Impossible," you might say. "The U.S. will defend Saudi Arabia at all costs." Indeed we will, but we had a similar commitment to Iraq last year — and ISIS drove right through it. Months of intensive air strikes still haven't expelled them from Anbar province, which borders Saudi Arabia.

The Saudis are clearly afraid of ISIS and its Iranian friends. They're frantically fortifying their northern border with fences, earthen berms and the same expensive surveillance equipment the U.S. uses on our own southern border. We know how well that works.

ISIS may have already found its way across the border. Three weeks ago, the Saudi general in charge of border security, Oudah al-Belawi, died in a suicide attack at the Suweif border post near Arar, according to The Telegraph.

We don't know that ISIS was responsible for the attack. We do know ISIS controls the territory on the other side of that border post, so it's fair to assume they cooperated, at least.

Notice a few other implications. Suicide bombers don't grow on trees, even for ISIS. Smart terrorist leaders use their limited supply of such people carefully, on high-priority targets. Killing this particular general must have been high on the list.

Notice also that the suicide bomber was in the right place at the right time to achieve the objective. Someone on the Iraqi side knew ahead of time that General al-Belawi was visiting the border post. That means they have reliable intelligence assets inside Saudi forces.

All this happened while Saudi King Abdullah was on his deathbed. He died last week and his brother Salman now holds the throne. Does he hold actual power? It's hard to say, given the kingdom's complicated internal politics, but it's a good bet that not everyone in the Saudi hierarchy is completely loyal to the new leadership.

The new leader, in turn, is probably uncertain whom he can trust. This, plus the fact that Saudi Arabia's oil-producing regions have a majority Shia population, ought to make Salman nervous. Maybe that's why President Obama is cutting short his India visit to "pay respects" to the late Abdullah and confer with Salman.

I don't buy the White House story, by the way. Note that the original plan was for Vice President Biden to go meet Salman, since Obama was busy with another important ally. Something made that plan unacceptable — something important enough to justify annoying India.

ISIS fancies itself the new Caliphate. Capturing control of holy cities Mecca and Medina plus Saudi Arabia's oil wealth would earn the group undying loyalty from millions more Muslims.

Such a feat would also make ISIS an even greater global nightmare. ISIS forces crossing into Saudi Arabia would certainly send oil prices soaring — and undermine the case for European quantitative easing and global economic recovery.

Just to make matters more interesting, higher oil prices would help Russian President Vladimir Putin out of his present economic jam.

I don't have any special insight on ISIS' strategy, but they have an opportunity to do something dramatic. We know they are good at seizing opportunities. If they choose to go after this one, I'm not sure anyone can stop them.

The odds still favor oil prices staying low this year, but a single curve ball could change the game. ISIS is warming up in the bullpen.